I have noticed the following 2 different forms for the Sturm-Liouville equation online, in different texts, and in lectures. [itex][p(x) y']'+q(x)y+\lambda r(x) y = 0[/itex] [itex]-[p(x) y']'+q(x)y+\lambda r(x) y = 0[/itex] Does it make a difference? I am guessing not as the negative can just be absorbed into function [itex]p(x)[/itex]? But I am still scratching my head as to why some texts use the negative sign in front of the 1st term. Is there some advantage to doing so? Thanks in advance.